Levitating magnet provides new nuclear fusion technique

Emma Woollacott, 25th January 2010

A new experiment to reproduce planetary magnetic fields could be an important step towards nuclear fusion.

The Levitated Dipole Experiment, or LDX, a joint project of MIT and Columbia University, uses a half-ton donut-shaped magnet made of superconducting wire coiled inside a stainless steel vessel.

The magnet is suspended by a powerful electromagnetic field, and is used to control the motion of the 10-million-degree-hot plasma contained within its outer chamber.

The results confirm that inside the device's magnetic chamber, random turbulence causes the plasma to become more densely concentrated — a crucial step in achieving fusion — instead of dissipating.

This 'turbulent pinching' of the plasma has been observed in the way plasmas in space interact with the Earth's and Jupiter's magnetic fields, but has never before been recreated in the laboratory.

MIT senior scientist Jay Kesner cautions that the kind of fuel cycle planned for other types of fusion reactors such as tokamaks, which use a mixture of two forms of 'heavy' hydrogen called deuterium and tritium, should be easier to achieve and will likely be the first to go into operation.

The deuterium-deuterium fusion planned for devices based on the LDX design, if they ever become practical, would likely make this "a second-generation approach," he says.

When operating, the huge LDX magnet is supported by the magnetic field from an electromagnet overhead, which is controlled continuously by a computer based on precision monitoring of its position using eight laser beams and detectors.

Levitation is crucial because the magnetic field used to confine the plasma would be disturbed by any objects in its way, such as any supports used to hold the magnet in place.

The scientists say that if the turbulence-induced density enhancement could be scaled up to larger devices, it might enable them to recreate the conditions necessary to sustain fusion reactions.